LITTLE CHAH6EABOUT. 15 



still alive and active, sustained, no doubt, by the water which 

 finds its way to them from above ! 



But perhaps the most curious situation in which these remains 

 have yet been found is in the guano which is brought from the 

 coast of Africa and Peru. Great numbers of the frustules have 

 been found in this material ; and it has been conjectured,* with 

 considerable probability, that the peculiar value of guano in the 

 growth of cereals may greatly depend on the presence of these 

 minute organisms, inasmuch as they supply it with that extra 

 amount of silica which all the corn-plants require. Thus, if this 

 conjecture be well founded, these minute beings, after perform- 

 ing their part in the economy of nature while alive, and then 

 lying entombed amidst a feculent mass of animal exuviai for 

 perhaps thousands of years, at length reappear, to add fertility 

 to our fields, and to multiply the means of human subsistence. 



Leaving, now, those sections of these microscopic forms of 

 life which have been handed over to the botanist as properly be- 

 longing to the Vegetable Kingdom, we pass on to the true Animal- 

 cules. We have already seen, however, how vague and inappro- 

 priate is this term, as referring solely to the minute size of the 

 organisms embraced by it, and in no degree marking their grade 

 in the scale of being. The reader will not be surprised, there- 

 fore, to learn that this term is now discarded as of no value, 

 while for the simplest of these truly animal forms which were 

 originally comprehended by it, the name of Protozoa has been 

 adopted ; thus marking their position at the very base of the 

 animal series, as the corresponding name ProtopTiyta expresses 

 the rank of the simplest forms of vegetable life. 



Beginning our survey of the Protozoa with those lowest in the 

 scale, we take the little Amoeba (Amceba dijfluens), formerly 

 known as the Proteus, and famous amongst microscopical obser- 

 vers for its incessant change of form. This little creature is com- 

 monly to be met with at the bottom of ponds of clear water, and 

 to the naked eye appears a mere animated dot of jelly. It is re- 

 markable for the extraordinary simplicity of its structure, consist- 

 ing wholly of a granular gelatinous substance named sarcode, and 

 having neither head, nor mouth, nor stomach, nor special organs 

 of any kind whatsoever. It has not so much even as an investing 

 membrane or skin, its outer surface exhibiting no trace of any 

 structure at all firmer in consistence than the rest of the body. 



